There are many applications in the prior art that require the selective switching between optical fibers, wherein a signal traveling along a source fiber is selectively directed to a number of other optical fibers. One such prior art application is optical time domain reflectometry (OTDR), wherein fiber link integrity is monitored by sending short optical pulses into fibers and measuring the back reflections as a function of time. In OTDR, the light source of a testing apparatus is selectively coupled to the fibers in a network, thereby providing a means for testing each of the fibers within the network. However, in order to test all of the fibers contained within a network, the output of the testing light source must be switched to each of the fibers in the network during the testing period.
During an OTDR testing procedure, a single OTDR testing apparatus is typically shared by a large number (N) of fibers in a network using a 1.times.N switching arrangement. Arbitrarily large switches have been constructed from smaller banks of optomechanical switches. However, as the smaller banks of optomechanical switches are combined, the cost of the switching configuration grows proportionately.
A simple way to provide optical fiber switching has been to perform the switching manually, via manually operated switchboard panels. Such switchboard panels use mechanically manipulated connectors. However, the use of mechanically operated switchboard panels is limited to applications where the number of fibers to be switched is relatively small and a slow switching time is acceptable.
Switching applications that require a rapid switching response and include a large number of optical fibers, typically use automated switching devices. Certain optomechanical switches have a switching response of the order 10 ms-50 ms, which is far more rapid than is possible for a manually operated switchboard panel. Furthermore, optomechanical switches have good crosstalk, back reflection, insertion loss characteristics and are relatively inexpensive compared to faster integrated optics switches. In optomechanical switches, a lensed input fiber is mechanically moved across a bank of lensed output fibers. As the lensed input fiber passes each lensed output fiber, the optical signal from the lensed input fiber is optically transferred to the lensed output fiber.
Since optomechanical switches require that a lensed input fiber be mechanically moved across a bank of lensed output fibers, optomechanical switches are well adapted for applications where output fibers in a bank are sequentially coupled to a source fiber, such as in the previously described OTDR testing procedure.
For conventional optomechanical switches, microlenses must be aligned to each fiber being tested. In other conventional switching arrangements, such as those that use electro-optic waveguides, alignment procedures to align the switching device to each fiber being tested must also be employed. In applications requiring larger switches, the cost of fiber alignment is the dominant cost, wherein the cost of aligning the switching device is more expensive than the switching device itself. As a result, the overall cost of using a switching assembly has been directly proportional to the number of fibers to be switched.
In MULTIPOSITIONAL OPTICAL-FIBRE SWITCH, by Tomlinson et al., ELECTRONICS LETTERS, Vol. 15, No. 6 pp. 192 et seq. (15 Mar. 1979), an optical switch is disclosed that employs a free space optical arrangement, wherein a signal from a source fiber is reflected through an optical system and redirected to other fibers. This switch uses of a quarter period graded-refractive-index rod lens, wherein the input and the output fibers are arranged in a circular configuration. An input fiber is placed at the center of the graded-refractive-index rod lens. The signal from the input fiber passes through the center of the lens, reflects off a rotating mirror and is directed to one of the output fibers that are positioned along a circular path around the center input fiber. However, achieving and maintaining optical alignment of the circular configuration is difficult and costly. This switch configuration is also limited in its application because the spot positioning accuracy is insufficient for single mode fibers.
A need therefore exists in the art for a low cost optical fiber switch that is capable of rapidly switching a large number of fibers and does not require individual fiber alignment, yet is adaptable to a wide variety of fiber configurations such as optical time domain reflectometry testing applications for fiber networks.